Superdense cosmological dark matter clumps

TL;DR

This paper investigates the formation, evolution, and observational prospects of superdense dark matter clumps, highlighting their potential detection via gamma rays and gravitational waves, and discussing constraints from primordial black holes.

Contribution

It introduces new models for the formation and evolution of superdense dark matter clumps, including their density profiles and potential observational signatures.

Findings

Superdense clumps can form from inflationary perturbations and phase transitions.

Clumps with electroweak-scale DM evolve into a power-law density profile.

Superheavy DM clumps may undergo gravithermal catastrophe, forming a denser core.

Abstract

The formation and evolution of superdense clumps (or subhalos) is studied. Such clumps of dark matter (DM) can be produced by many mechanisms, most notably by spiky features in the spectrum of inflationary perturbations and by cosmological phase transitions. Being produced very early during the radiation dominated epoch, superdense clumps evolve as isolated objects. They do not belong to hierarchical structures for a long time after production, and therefore they are not destroyed by tidal interactions during the formation of larger structures. For DM particles with masses close to the electroweak (EW) mass scale, superdense clumps evolve towards a power-law density profile $\rho(r) \propto r^{-1.8}$ with a central core. Superdense clumps cannot be composed of standard neutralinos, since their annihilations would overproduce the diffuse gamma radiation. If the clumps are constituted of superheavy DM particles and develop a sufficiently large central density, the evolution of their central part can lead to a 'gravithermal catastrophe.' In such a case, the initial density profile turns into an isothermal profile with $\rho \propto r^{-2}$ and a new, much smaller core in the center. Superdense clumps can be bserved by gamma radiation from DM annihilations and by gravitational wave detectors, while the production of primordial black holes and cascade nucleosynthesis constrain this scenario.